1. Field of the Invention
The present invention relates to an image heating apparatus for heating an image formed on a sheet.
2. Description of the Related Art
Conventionally, there exists a belt fixing type fixing apparatus (image heating apparatus) which uses a fixing belt to heat and pressurize a toner image formed by an image forming apparatus such as an electrophotographic apparatus and an electrostatic recording apparatus to fix the toner image.
As the belt fixing type fixing apparatus, there is known a fixing apparatus using a fixed contact member which rubs an inner surface of a belt, such as a pressure pad for applying a pressure to the belt from its inner side and a belt guide for guiding the belt. In this fixing apparatus, a sliding frictional resistance between the inner surface of the belt and the fixed contact member increases to prevent stable running of the belt and stable conveying properties of a sheet such as paper. As a result, there is a fear that a sheet jam or an image defect due to slippage of the belt or the sheet may occur. Moreover, when the sliding frictional resistance is large, a driving torque becomes large, which causes damage to a gear (introducing drive). Therefore, reduction of the sliding frictional resistance by supplying a lubricant such as grease or oil on the inner surface of the belt has been proposed (Japanese Patent Application Laid-Open No. H10-213984). Moreover, a configuration for stably supplying a small amount of the lubricant to a lubricant applied member by providing a porous member such as polytetrafluoroethylene (PTFE) on a surface of a roller-shaped lubricant retaining member and abutting the porous member against the lubricant applied member to rotate the porous member has also been proposed (Japanese Patent Application Laid-Open No. H09-185282).
Further, a configuration of providing a lubricant applying roller as described above on the inner surface of the belt to reduce a sliding resistance between the inner surface of the belt and a fixed sliding member has been proposed (Japanese Patent Application Laid-Open No. 2007-079036).
However, the fixing apparatus using the lubricant applying roller as the lubricant applying member as described above has the following problems.
For stably applying a small amount of the lubricant onto the inner surface of the belt, the lubricant applying roller includes a lubricant retaining portion for retaining the lubricant and a lubricant applying amount regulating layer made of a porous material formed on a surface of the lubricant retaining portion. The lubricant applying amount regulating layer is generally made of a porous resin sheet material such as a nonwoven fabric formed by fiber of polytetrafluoroethylene (hereinafter, referred to as PTFE), polyimide, or polyamide-imide and a resin such as polyester.
On the other hand, it is desirable that the lubricant applied member (inner surface of the belt) has a surface slidability as small as possible to reduce the sliding resistance between the lubricant applied member and the fixed member. Therefore, the sliding resistance in an abutting portion between a surface of the lubricant applying roller and the inner surface of the belt serving as the lubricant applied member becomes smaller. As a result, it becomes difficult to obtain a sufficient rotary driving force of the lubricant applying roller, which destabilizes the application of the lubricant.
It is conceivable to increase an abutment pressure of the lubricant applying roller to obtain the sufficient rotary drive of the lubricant applying roller. When the abutment pressure is increased, the rotation of the lubricant applying roller becomes stable. At the same time, however, an applying amount of the lubricant is increased. As a result, the lubricant is used up in a short period of time. Moreover, if the amount of the lubricant applied on the inner surface of the belt is large, the lubricant leaks from an end of the belt. The leaking lubricant flows to a surface of the belt to cause an image defect.
It is also conceivable to directly drive (introduce direct drive to) the lubricant applying roller. However, there is a fear that a configuration of the image heating apparatus is complicated to increase the size of the image heating apparatus itself.